This application relates to fiber lasers, and in particular, to actively mode-locked fiber lasers.
A fiber laser may use one or more optical fiber segments to form an optical resonator. At least one portion of the fiber in the resonator is doped with active ions (e.g., Er ions) to form the laser gain medium for producing the optical gain for the laser oscillation in the resonator when optically pumped by light at a pump wavelength. The fiber laser generally produces a laser beam at a laser wavelength longer than the pump wavelength.
Pulsed fiber lasers are of particular interest in many applications, such as optical fiber communication systems. A mode locking mechanism may be implemented in a fiber laser to lock multiple laser modes for producing laser pulses when the resonator supports multiple laser modes. This mode locking may be either active or passive. In active mode locking, the intracavity optical field is modulated at a frequency equal to one or a multiplicity of the mode spacing. In passive mode locking, at least one nonlinear optical element is placed inside the laser cavity to produce an intensity-dependent response to an optical pulse so that the pulse width of the optical pulse exiting the nonlinear element is reduced.
This application discloses mode-locked fiber lasers where the optical dispersion within the optical resonator is managed to control the frequency chirp characteristics and pulse shape of output laser pulses. The frequency chirp and pulse shape may be controlled in a way to negate adverse effects on the optical pulses such as dispersion caused by transmission through a fiber link and hence increase the transmission distance of the optical pulses without pulse reconditioning by an optical relay device in the fiber link.